Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Multiple days of snowfall and wind loading make for dangerous avalanche conditions.  Natural and remotely triggered avalanches on Friday illustrate the deadly threat.  Leeward terrain is the most dangerous and should be avoided.  Natural avalanches are possible on slopes with active loading or solar warming.  Sheltered terrain harbors an untrustworthy layer of surface hoar around 2 feet deep that has been responsible for recent avalanches and accidents.  Lower elevation sunny slopes are less likely to have the problematic weak layer but avalanches could fail in the recent storm.  Conservative slope angles are your best defense against a dangerous avalanche in sheltered areas.  You can always select terrain less than 30 degrees to manage the avalanche hazard and enjoy the fresh snow.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs about 2 feet thick over these weak layers can be triggered by skiers and riders. This avalanche problem can be remotely triggered from flat terrain, or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is isolated potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

    You can reliably avoid trouble by selecting terrain with slope angles less than 30 degrees that are free from overhead steep terrain.

     

    This skier-triggered persistent slab avalanche likely failed on a layer of buried surface hoar last weekend.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2

    Since last Wednesday, 12,000ft weather stations have recorded westerly winds averaging into to 20mph range and gusting into the 30's to 50's mph range. Steady snowfall has continued to keep snow available for transport onto lee terrain features. This has created dangerous wind slabs and is further loading persistent weak layers buried deeper in the snowpack. Natural avalanche activity is possible during periods of heavy precipitation rates or active wind-loading.  Avalanches that start in recently drifted storm snow could "step down" and release a much larger avalanche. 

    An example of a large avalanche that failed on a wind-loaded terrain feature last week.

Avalanche Discussion

Avalanche conditions are dangerous in the Northwest and Southeast Mountains forecast zones.  Snowfall from Wednesday through Saturday morning has resulted in accumulations of a foot in most areas with some places in the Northwest Mountains even deeper.  Snow water equivalents range from about 1.6 inches to 1 inch.  Now factor in consistent westerly winds drifting all the new snow and you have a recipe for dangerous avalanche conditions.  Even with poor visibility on Friday, ample evidence was observed of the dangerous conditions like this remotely triggered avalanche on Axtel, these avalanches on Schuylkill Ridge, and natural activity immediately adjacent to town on Gibson Ridge.  Natural avalanche activity may continue today from drifting or solar warming due to clear skies.

There are two broad types of terrain you will want to avoid today to reduce the chances of triggering a dangerous avalanche.  First, avoid terrain with evidence of recent drifting.  These slopes will be commonly found at upper elevations where westerly winds transported snow, but could be found in isolated places at lower elevations.  Enough mass exists in just the storm snow to be problematic where drifted into thicker slabs.  Avalanches that break on weak layers below the recent storm snow could grow to very large sizes on some leeward slopes and be difficult to survive.

The second type of terrain to avoid is steep slopes highlighted by the Persistent Slab rose including sheltered areas.  There is some uncertainty about the impact of the recent snow on the buried surface hoar and the likelihood of releasing a deadly avalanche in sheltered locations.  The natural avalanches on Gibson Ridge point to increased sensitivity particularly for areas in the Southeast Mountains where the snowpack is generally shallower.  Surface hoar is a notoriously tricky layer and one we don't commonly deal with in the Crested Butte area.  The evidence and uncertainty point to making conservative terrain choices wherever you expect to encounter or find buried persistent weak layers.

Low elevation sunny slopes are the least likely place to encounter problematic surface hoar or facets, however, there is enough recent snow that you will need to make thoughtful decisions and skillful assessment of the snowpack before entering steeper terrain.

Regioni coperte